Thermal dye transfer printing process for reducing curling of a print sheet

Abstract

A thermal dye transfer printing process for making transparent prints, which comprises bringing a dye-bearing donor ribbon (17) in contact with a dye-receiving polymer print sheet (15) at a print zone, supporting both materials on a backing support (14) in said zone and contacting the donor ribbon with a print head (18) for image-wise heating the ribbon and cause dye transfer to the print sheet, wherein the rear side of the print sheet is uniformly heated on a drum (30) after removal of the sheet from the backing support, thereby to reduce curling of the sheet caused by the image-wise heating of its front side.

We claim: 
     
       1. A thermal printing process for making transparent prints comprising: supporting a printing substrate having a front side and a rear side on a rotatable print drum such that the rear side contacts the rotatable print drum; thermal printing on the front side of the printing substrate by rotating the rotatable print drum at a printing speed while image-wise energizing a thermal print head thereby heating the front side of the printing substrate and forming an image on the front side of the printing substrate; subsequently conveying the printing substrate onto a heated roller having a peripheral surface wherein the rear side of the printing substrate contacts the peripheral surface of the heated roller thereby heating the rear side of the printing substrate and simultaneously rotating the heated roller at a peripheral speed wherein the peripheral speed is independent of the printing speed, further comprising adjusting the peripheral speed as a function of the heating of the front side of said printing substrate. 
     
     
       2. A thermal printing process for making transparent prints comprising: supporting a printing substrate having a front side and a rear side on a rotatable print drum such that the rear side contacts the rotatable print drum; thermal printing on the front side of the printing substrate by rotating the rotatable print drum at a printing speed while image-wise energizing a thermal print head thereby heating the front side of the printing substrate and forming an image on the front side of the printing substrate; subsequently conveying the printing substrate onto a heated roller having a peripheral surface wherein the rear side of the printing substrate contacts the peripheral surface of the heated roller thereby heating the rear side of the printing substrate and simultaneously rotating the heated roller at a peripheral speed wherein the peripheral speed is independent of the printing speed, further comprising adjusting the heating of the rear side of the printing substrate as a function of the heating of its front side.